May 01
Scientists Create First Memristor: Missing Fourth Electronic Circuit Element
By Bryan Gardiner 
April 30, 2008 | 12:03:41 PMCategories: Research
Researchers at HP Labs have built the first working prototypes of an important new electronic component that may lead to instant-on PCs as well as analog computers that process information the way the human brain does.
The new component is called a memristor, or memory resistor. Up until today, the circuit element had only been described in a series of mathematical equations written by Leon Chua, who in 1971 was an engineering student studying non-linear circuits. Chua knew the circuit element should exist -- he even accurately outlined its properties and how it would work. Unfortunately, neither he nor the rest of the engineering community could come up with a physical manifestation that matched his mathematical expression.
Thirty-seven years later, a group of scientists from HP Labs has finally built real working memristors, thus adding a fourth basic circuit element to electrical circuit theory, one that will join the three better-known ones: the capacitor, resistor and the inductor.
Researchers believe the discovery will pave the way for instant-on PCs, more energy-efficient computers, and new analog computers that can process and associate information in a manner similar to that of the human brain.
According to R. Stanley Williams, one of four researchers at HP Labs' Information and Quantum Systems Lab who made the discovery, the most interesting characteristic of a memristor device is that it remembers the amount of charge that flows through it.
Indeed, Chua's original idea was that the resistance of a memristor would depend upon how much charge has gone through the device. In other words, you can flow the charge in one direction and the resistance will increase. If you push the charge in the opposite direction it will decrease. Put simply, the resistance of the devices at any point in time is a function of history of the device –- or how much charge went through it either forwards or backwards. That simple idea, now that it has been proven, will have profound effect on computing and computer science.
"Part of what's going to come out of this is something none of us can imagine yet," says Williams. "But what we can imagine in and of itself is actually pretty cool."
For one thing, Williams says these memristors can be used as either digital switches or to build a new breed of analog devices.
For the former, Williams says scientists can now think about fabricating a new type of non-volatile random access memory (RAM) – or memory chips that don't forget what power state they were in when a computer is shut off.
That's the big problem with DRAM today, he says. "When you turn the power off on your PC, the DRAM forgets what was there. So the next time you turn the power on you've got to sit there and wait while all of this stuff that you need to run your computer is loaded into the DRAM from the hard disk."
With non-volatile RAM, that process would be instantaneous and your PC would be in the same state as when you turned it off.
Scientists also envision building other types of circuits in which the memristor would be used as an analog device.
Indeed, Leon himself noted the similarity between his own predictions of the properties for a memristor and what was then known about synapses in the brain. One of his suggestions was that you could perhaps do some type of neuronal computing using memristors. HP Labs thinks that's actually a very good idea.
"Building an analog computer in which you don't use 1s and 0s and instead use essentially all shades of gray in between is one of the things we're already working on," says Williams. These computers could do the types of things that digital computers aren't very good at –- like making decisions, determining that one thing is larger than another, or even learning.
While a lot of researchers are currently trying to write a computer code that simulates brain function on a standard machine, they have to use huge machines with enormous processing power to simulate only tiny portions of the brain.
Williams and his team say they can now take a different approach: "Instead of writing a computer program to simulate a brain or simulate some brain function, we're actually looking to build some hardware based upon memristors that emulates brain-like functions," says Williams.
Such hardware could be used to improve things like facial recognition technology, and enable an appliance to essentially learn from experience, he says. In principle, this should also be thousands or millions of times more efficient than running a program on a digital computer.
The results of HP Labs teams findings will be published in a paper in today's edition of Nature. As far as when we might see memristors actually being used in actual commercial devices, Williams says the limitations are more business oriented than technological.
Ultimately, the problem is going to be related to the time and effort involved in designing a memristor circuit, he says. "The money invested in circuit design is actually much larger than building fabs. In fact, you can use any fab to make these things right now, but somebody also has to design the circuits and there's currently no memristor model. The key is going to be getting the necessary tools out into the community and finding a niche application for memristors. How long this will take is more of a business decision than a technological one."
Image: An atomic force microscope image of a simple circuit with 17 memristors lined up in a row. Each memristor has a bottom wire that contacts one side of the device and a top wire that contacts the opposite side. The devices act as 'memory resistors', with the resistance of each device depending on the amount of charge that has moved through each one. The wires in this image are 50 nm wide, or about 150 atoms in total width. Image courtesy of J. J. Yang, HP Labs.
科学家创造了第一个Memristor：遗失的第四种电子电路元件
作者: Bryan Gardiner
翻译：apollo_maverick
注：memristor来自于memory resistor（记忆电阻器），还没有正式的译法，以下都译为忆阻器）
HP Labs的研究者已经制造了一种重要的新电子组件的第一个可以工作的原形，这种电子组件可能使即开型PC（instant-on PCs）以及以像人类大脑处理信息的方式的模拟式计算机（analog computers）成为可能。
这种新组件被叫做忆阻器，或记忆电阻器（memory resistor）。直到今天以前，这种电路元件都只是被Leon Chua写的一组数学方程式描述的，在1971年，Leon Chua是一个研究非线性电路的工程学生。Chua知道这种电路元件应该存在——他甚至精确地描述了它的特性和它如何工作。不幸的是，他以及其他的工程团体都未能搞出符合他的数学表达的物理实现。
37年后，HP Labs的一组科学家最终造出了真正的可以工作的忆阻器，因此把第四种基本电路元件加入了电子电路理论，另外三个广为所知的是：电容器，电阻器和电感器。
根据R. Stanley Williams，HP Labs信息与量子系统实验室搞出这个发现的四位研究者之一，的说法，忆阻器器件的最有趣特征是它可以记忆流经它的电荷数量。
研究者相信这个发现将为即开型PC、更高能效的计算机和以人类大脑类似方式处理和联系信息的模拟式计算机铺平道路。
的确，Chua起初的想法是忆阻器的电阻取决于多少电荷经过了这个器件。也就是说，你能让电荷以一个方向流过，电阻会增加。如果你让电荷以反向流动，电阻就会减小。简单地说，这种器件在任一时刻的电阻是时间的函数（译者注：原文为“the resistance of the devices at any point in time is a function of history of the device”）——或多少电荷向前或向后经过了它。那个简单的想法，现在已经被证实，并将对计算及计算机科学产生深远的影响。
“这将导致什么出现是任何人都还无法想像的，”Williams说，“但我们可以想像的是这个东西本身确实很酷。”
举个例子，Williams说这些忆阻器可以用于数字式开关（digital switches）或制造新型的模拟器件（a new breed of analog devices）。
相较于过去，Williams说科学家现在可以考虑构造新型的非易失性随机存取存储器（RAM）——或当计算机关闭后不会忘记它们曾经所处的能量状态的存储芯片。
那是今天的DRAM所面临的大问题，他说。“当你关闭你的PC电源，DRAM就忘记了那里曾有过什么。所以下次打开计算机电源你就必须坐在那儿等到所有需要运行计算机的东西都从硬盘装入到DRAM。”
有了非易失性RAM，那个过程将是瞬间的并且你的PC会回到你关闭时的相同状态。
科学家也预想制造其他类型的电路，忆阻器在其中可以用作模拟器件（analog device）。
的确，Leon自己注意到了在他自己预言的忆阻器的特性与他知道的大脑的突触之间的相似性。他的一个建议是你可能用忆阻器做某种类型的神经计算。HP Labs认为那确实是个非常好的想法。
“制造一个模拟式计算机，在其中不用1和0的，而代之的是用就像明暗不同的灰色之中的几乎所有状态（instead use essentially all shades of gray in between），这是我们正在做的事情中的一件，”Williams说。这些计算机可以做许多种数字式计算机不很擅长的事情——比如做决策，判定一个事物比另一个大，或甚至学习。
当前就有许多研究者试图编写在标准机器上运行的计算机代码来模拟大脑功能，他们必须使用大量的有巨大处理能力的机器来模拟仅仅是大脑的很小的部分。
Williams和他的团队说他们现在能用一种不同的方式：“不同于写计算机程序来模拟大脑或模拟大脑的某种功能，我们事实上依靠构造某种基于忆阻器的仿真类大脑功能的硬件，”Williams说。
这样的硬件可以用来改进一些事情，比如脸部识别技术，并且使本质上从经验来学习的装置可用，他说。基本上，这也应该是比在数字式计算机上运行程序要快几千到几百万倍。
HP Labs团队发现的结果将被公布在一篇今天的《自然》杂志论文中。直到我们可以看到忆阻器真正被用于实际的商业器件中，Williams说相较于技术上的限制，限制更多来自于商业上。
最终，这个问题将与投入到设计忆阻器电路的时间和努力有关，他说。“投资到电路设计上的钱的确比建造工厂多得多。事实上，你现在就可以用任何工厂来做这些东西，但是也必须设计电路而且目前还没有忆阻器的模型。关键是搞出必要的工具并且为忆阻器找到合适的应用。这要多久更多的是个商业决策问题较于技术问题。”
图片：原子力显微镜下的一个有17个忆阻器排列成一排的简单电路的图像。每个忆阻器有一个底部的导线与器件的一边接触，一个顶部的导线与另一边接触。这些器件起“记忆寄存器（memory registors）”的作用，每个器件的电阻取决于通过每个器件上的电荷数量。这幅图中的这些导线是50nm宽，或总共大约150个原子宽。图片由J. J. Yang, HP Labs许可。
转自：http://blog.wired.com/gadgets/2008/04/scientists-prov.html
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